Relationship of Chlorophyll Biosynthetic Heterogeneity to the Greening Group Affiliation of Plants - Chlorophyll Biosynthesis and Technological Applications - page 314

Pchlide a that accumulate in daylight. While monocotyledonous DMV-LMV plants
accumulate mainly MV Pchlide a in daylight, under the same conditions, monocot-
yledonous DM-LDV plants accumulate mainly DV Pchlide a . The possible rela-
tionship of this difference between the two greening groups of plants to the rates of
DV and MV Pchlide a biosynthesis in daylight was therefore investigated by
determining the light-dark-rate of MV and DV regeneration during the light
phase of the photoperiod.
As reported in Table 14.2 , in all DMV-LDV and DMV-LMV species that were
examined, the observed rates of MV Pchlide a regeneration upon returning the
plants from light to darkness were much higher than those of DV Pchlide a during
the first 5 min of dark-Pchlide a regeneration and thereafter. The same was also true
after 30 and 60 min of dark-Pchlide a regeneration (Table 14.2 ).
These results strongly suggested that in both DMV-LMV and DMV-LDV
monocotyledonous plants, the MV Chl a biosynthetic route is the dominant route
in daylight. As a consequence DMV-LMV plants such as Jhonsongrass are and
DMV-LDV were assigned to a DMV-LMV-LDMV greening group.
Figure 14.3 summarizes the greening group affiliation of plants and take into
account the Dar-Light Chl biosynthetic routes involvement in the process.
If the DV/MV Pchlide a ratio for a plant species is larger than 1, for a particular
phase of the photoperiod, then the plant is considered to be DV for that phase of the
photoperiod. If the ratio is less than one, the plant is considered to beMV for that phase
of the photoperiod. Plants that are DV during the dark phase of the photoperiod are
referred to as DDV. Plants that are MV during the dark phase of the photoperiod
are referred to as DMV. Likewise Plants that are DV during the light phase of the
photoperiod are referred to as LDV. Plants that are MV during the light phase of the
photoperiod are referred to as LMV. Plants that accumulateDVPchlide a immediately
after returning them from light to darkness are referred to as LDDV. Plants that
accumulate MV Pchlide a immediately after returning them from light to darkness
are referred to as LDMV. As a consequence for plants can be classified as DDV/LDV/
LDDV, DMV/LDV/LDMV or DMV/LMV/LDMV.
14.4 Biological Significance of the Greening
Group Affiliation of Green Plants
Natural selection has often produced multiple (bio) chemical and physical ways of
conveying the same message. Genetic redundancy achieves the same purpose. It is
therefore logical to thing of the Chl biosynthetic heterogeneity as a hedge against
lethal mutations.
It is also possible that via natural selection, Chl biosynthetic heterogeneity has
imparted an evolutionary advantage to higher plants. As was just described, the
preferential operation of the MV or DV Chl a monocarboxylic biosynthetic routes
during the formation of Chl a in higher plants is a species-dependent phenomenon
with evolutionary significance (Abd-El-Mageed et al. 1997 ; Ioannides et al. 1994 ).